1. Field of the Invention
This invention relates in general to high frequency high power semiconductor devices and, more particularly, to high frequency high power transistor device assemblies having improved performance.
2. Background Art
High power high frequency semiconductor devices are widely used. In many circumstances it is essential that high power, i.e., in the range of several hundred watts, be provided at frequencies extending into the HF and VHF ranges (3-300 MHz) in a single device assembly. Most commonly, devices operating in these power and frequency ranges are fabricated from several semiconductor die operating electrically in parallel within a single housing or assembly.
In the prior art, devices capable of operating at power levels of approximately 500 watts at 2-30 MHz have been achieved. The type TH-20 transistor assembly manufacture by Thompson-CSF of Paris, France is a typical example. Higher power and higher frequency operation are much desired. Further, prior art devices have suffered from a number of limitations, in particular, poor thermal dissipation requiring the use of water cooled assemblies to carry away the heat, the use of large numbers of complex internal parts and the high cost thereof, the use of an excessive number of welded or solder internal connections which adversely affect the reliability of the unit, and the absence of chip-to-chip ballasting resistors to insure uniform current distribution in multi-chip designs. Thus, a need continues to exist for high frequency high power devices which will simultaneously achieve higher powers and higher operating frequencies, while avoiding water cooling and complex, expensive internal structures that need large numbers of welded or soldered connections, and which incorporate inter-chip ballasting resistors to equal chip currents.
Accordingly, it is an object of the present invention to provide an improved high power and high frequency semiconductor device assembly having power and frequency capabilities equal or greater than heretofor achieved.
It is an additional object of the present invention to provide an improved high power and high frequency device assembly in which the number of internal piece parts and the number of internal interconnections has been substantially reduced.
It is a further object of the present invention to provide an improved high frequency and high power device assembly in which the thermal performance is such as to eliminate the need for water cooling.
It is an additional object of the present invention to provide an improved high frequency and high power transistor assembly having a more compact internal arrangement so that lead length is minimized in order to achieve lower inductance.
It is a further object of the present invention to provide an improved high frequency and high power transistor assembly wherein the above advantages are achieved simultaneously.
As used herein the words "metal" or "metallic" are intended to refer to any highly electrically conductive material whether semiconductor, semimetal, intermetallic, or metal. The words "bond" or "bonding" are intended to refer to any metallurgical means for joining objects, including but not limited to soldering, eutectic bonding, brazing, or welding, and under circumstances where electrical conductivity is not required, the use of dielectric solders or adhesives such as but not limited solder glasses or epoxies. As used herein the words "wire bonds" are intended to refer to any form of interconnecting leads which extend in part above the surface to which they connect, whether round, flat, or tape mounted leads or incorporating bumps.